PSI - Issue 68

Lucia Morales-Rivas et al. / Procedia Structural Integrity 68 (2025) 493–499 Lucia Morales-Rivas, Eberhard Kerscher / Structural Integrity Procedia 00 (2025) 000–000

495 3

4 = 1 + ( # −1) .+ . , 0 -. 1 / 1( 2

(4) where is also the notch depth and ( ′ is a characteristic length parameter. Note that in ( ′ the apostrophe has been used in order to distinguish it from the EHST parameter, ( . 1.2. Notch effect on stress-strain distributions Apart from his work on the explanation of 1 , Neuber is known from his description of the plastic zone ahead of the notch root, when local stresses are high enough to cause yielding, postulating the most popular notch correction method, known as the Neuber’s rule -Neuber (1961)-. The Neuber´s rule states that the geometric mean of the stress and strain concentration factors is equal to the theoretical elastic stress concentration factor, ) . It means that the Neuber´s rule assumes that the total strain energy at the notch root of an actual elasto-plastic body is equal to the total pseudo (fictitious) strain energy density as if a material theoretically maintained its linear elastic behaviour -Neuber (1961), Ince and Bang (2017)-. That is, the product of the stress and the strain would be constant and equal to the product of the fictitious maximum elastic stress (σ max,fict ) and the fictitious maximum elastic strain (ε max,fict ).

Fig. 2.(a) Schematic illustrations of the Neuber’s rule, explained in the subsection 1.2; (b) Kitagawa-based diagrams as applied according to the explanation in the subsection 3.1, where is the crack size. Such a rule has frequently been applied for the determination of the fatigue life of notched specimens, through a local strain approach. For that purpose, after the estimation of the local stresses and local strains through Neuber´s rule considering the hysteresis stress-strain curve of the material (in smooth specimens), a selected algorithm is typically implemented in order to compute the damage generated at each step of the cyclic stress-strain path in the notched specimen -Visvanatha (1998)-. Although current analyses based on the Finite Element Method (FEM) for the determination of local stresses and strains can replace the more traditional empirical equations, the latter are often the simplest solution to solve many notched geometries. 2. Materials and experimental procedure In a preceding project, MECBAIN -Sourmail et al. (2017)-, different nanobainitic conditions were studied - information on this family of advanced bainitic steels can be found in refs. Caballero and Bhadeshia (2004), Bhadeshia (2010) and Garcia-Mateo et al. (2015), among others-. In the present work, the following microstructures will be considered, designated as: 0.6C-1.5Si-890°C-220°C (114h), 0.6C-1.5Si-890°C-250°C (16h), and 1C-2.5Si-950°C 250°C (16h) The names indicate the nominal C content and the nominal Si content in wt. %, the austenitization temperature, the austempering temperature (the temperature of the isothermal holding for bainitic transformation), and the duration of the austempering treatment. The complete chemical compositions and more details can be found in ref. Mueller et al. (2016). The values for the yield strength ( YS ), the ultimate tensile strength ( UTS ), and the stress